Mineral jigs are gravitational concentrators used widely in the mining industry to separate the mineral from the gangue material based on density differences in the separated materials. Mineral jigs have recently been used in soil decontamination processes such as those set forth in U.S. Pat. No. 5,128,068 to Lahoda et al., assigned to the assignee of the present invention, and which is incorporated herein in its entirety.
The operation of a mineral jig can either be in cocurrent or countercurrent mode. The countercurrent mode, as taught in U.S. Pat. No. 5,128,068 is typically preferred for soil decontamination. In the countercurrent mode, the material to be separated is fed as a slurry into the top section of the jig and the material then flows into the hindered settling bed. A rinsing solution is fed into the bottom of the jig and this solution flows within the jig in an upward fashion. The hindered settling bed conventionally contains a layer of heavy particulate aggregate material, called "ragging" that rests upon a supporting grate. The ragging is commonly composed of gravel or a stone mixture. A layer or plurality of layers of balls, such as steel, glass, or ceramic balls, is also frequently used in the bed area to aid the separation process. The heavier particulate material in the feed slurry penetrates through the ragging and the grate, flows counter to the rinse solution, and is withdrawn as a concentrate from the bottom of the jig. The lighter gangue is carried out of the top of the jig with the rinse solution as overflow material. The separation in the jig is facilitated by imparting a high frequency pulse/suction flow between 200 to 300 Hz to the solution within the jig below the bed. This pulse/suction flow is commonly imparted by use of a diaphragm.
The current operation of the jig under these conditions suffers from various process problems. Coarser particles which are to be separated can have densities similar to or lighter than the bed ragging and dense ball layer, and thus have a difficult time traversing these materials.
A particular problem is adjusting the aggregate ragging coupled with the ball material layer and the jig stroke length to achieve adequate separation. If the depth of the ragging materials is too great, then a longer stroke length is required to disrupt this bed to allow separation. However, the longer stroke length tends to disrupt the bed in such a way that the ragging repositions itself and channeling problems arise. This channelling can usually only be detected by monitoring the exit streams and thus is not detected immediately. If the stroke length is too short, the heavier, larger particles will not penetrate through the bed, resulting in the bed becoming packed and process flooding can occur with most of the material being carried away in the overflow. If the depth of the ragging materials is decreased, then the separation efficiency between the particulate materials decreases.
A need therefore exists to design an improved mineral jig for the separation of feed materials. The jig design should provide for a hindered settling area that aids in the separation of the heavy and gangue particulate materials without the problems of channelling or flooding within the bed area.